They kind of work but still don't couple the source of sound (diaphragm / cone) well with the air through which we hear the music. To do that you need a horn. That is what releases the efficiency / detail and accurate sound (if implemented properly)
Incidentally my upper mid and tweeter are but 20cms apart. The tweeter, upper mid and mid are all within less than 50cm so no big deal.
How many un-amp'd bands have you heard that have a single sound source - yeah right none!
I think if you consider the large surface area used to transmit vibration to the air, it is comparable to that of a horn system. Think about it, a small diaphragm moving a small amount to move a large area of air at the mouth of a horn, or a large area diaphragm moving a small amount to move a large amount of air. Both have high efficiency and both move the same amount of air. How they do it doesn't matter, does it?
I'd have to ask you to expand on the comment about detail. Why does a high sensitivity deliver more detail? A low sensitivity system will need higher signal gain, but the small details will be amped up just the same as the obvious sounds. It might even be argued that the greater signal gain required moved it further away from the noise floor of the equipment making details easier to hear.
I think 20cm is very significant, but that depends if you are concerned with getting near point-source speakers.
That doesn't necessarily mean point source speakers are pointless, lol. IMO point source is less about phase relationship of frequency bands, and more about dispersion in the horizontal and vertical axis. You hear this via reflections from the room. If the vertical axis sound has big holes in the response you will hear it by the room. Horns help reduce that I suppose but not eliminate it, and there will still be changes from vertical listening position movements.
All this is not to say multi-way horn systems are rubbish. Not at all. They do have negative points though and I think in general discussion should not be ignored quite so easily. If you like the sound in your specific case though, then ignore away.
Hand-waving for discussion: Steve's point about the large air load is a good one - it means that driver displacement is heavily damped, and the coupling efficiency high; both these things minimise distortion from the drivers which pretty much scales with current through the voicecoil and with driver displacement.Tenson said:Why does a high sensitivity deliver more detail? A low sensitivity system will need higher signal gain, but the small details will be amped up just the same as the obvious sounds. It might even be argued that the greater signal gain required moved it further away from the noise floor of the equipment making details easier to hear
(hence the holy wars over optimal horn profile I suspect!)
It's worth reading anything you can find written by Paul Klipsch when it comes to horns, there is plenty dotted around the Klipsch website and forum, but it takes a little hunting down (hence my not linking directly). To paraphrase what I can remember: he states the key advantages as lower distortion due to a combination of better efficiency, lower moving mass, higher mechanical rigidity, and better interfacing with the room - he was a very firm believer in the corner horn figuring it better to accept the room exists and to work with it rather than producing speakers that fight this inevitability by needing to be away from boundaries etc. He coupled the bass-loading to the room itself whilst using the directional nature of the mid and tweeter horns as an advantage, i.e. fire the sound straight at the listener, not all over the room, thus far less reflection issues. I am convinced this is why (to my ears at least) horns sound so much more direct, clean and focused than wide-dispersion speakers - the ears get the sound before the room reflections (the brain is far better at filtering out post-echo than pre-echo). Obviously there have been many advances in conventional speaker design since Klipsch carried out his pioneering work, and many fine examples, but I still find his logic pretty much flawless. He was one of audio's great thinkers IMO